TST TPMS o ring replacement project. Parts (10 pack) from Lowes. Better thicker seal tover original, improved protection, but anti thief cap will not spin freely. Fair trade for me The one on the left shows the thicker ring. More data in the toad pic album.

your new o rings are way too large, .... just two weeks ago, I changed the batteries on my TST TPMS for the first time, .... my order of six, contained o rings for the first battery change(seems like destroying them when opening the unit, is very common, almost expected), ... I called the company, because the new o rings looked way too small and I thought they had included the wrong ones, ... was assured they would stretch over the unit and in doing so, would result in an even smaller dia. needed for everything to seal and work correctly, ... I used a small amount of silicone paste when re-assembling, ... hoping by doing so, the next time I open the units, the o rings will not get damaged as they did the first time(and I can see yours did as well), .... the correct new ones can be ordered from the company

Yes, they are bigger. To big, I don't know. I did buy a bag of Nitrile 11mm x 1mm after seeing a previous post about the part. I did validated the factory size, see the pic in the toad album for a side by side comparision. I think factory o rings are over priced to say the least. Also the fragile nature of the seal prompted me to look at alternatives. The bigger o rings do not expand (or break) like nitrile but rather stay static in size and are used for compression. IMHO I think for 2.50 bucks it is worth the look. Maybe throw a box in the coach for field work...as 11 x 1 o rings may be locally sourced at NAPA or such, I doubt anyone will find them in the local big box while on the road...

still remembering how much my replacement o rings stretched and being so tiny in thickness, ... reminded me of rubber bands, I've just now gone on Amazon and searched "small rubber bands", ... amazing just how small some can be, and sure seems like the right size small rubber bands could substitute for these o rings, worth a try, ... links below just a sample of what I found, ...

Had to replace a battery and the O ring broke. Parts at home so just put it back together ~~ been working fine for 2 months. I'll put the 'parts' bag in the 5er and replace the ring in FL if I can recall which one.

Thanks for the offer. We bought the system and it's been sitting in the coach for 3 months now, partly because my husband works all the time but part because we don't feel qualified to install them. Do you think we should try or for $100 the tire store said they would put them on? We watched a video on you tube and probably need to go back again but if we try and get stuck it's nice to know someone is there to answer questions.
Thanks, Terry

Thanks for the offer. We bought the system and it's been sitting in the coach for 3 months now, partly because my husband works all the time but part because we don't feel qualified to install them. Do you think we should try or for $100 the tire store said they would put them on? We watched a video on you tube and probably need to go back again but if we try and get stuck it's nice to know someone is there to answer questions.
Thanks, Terry

Watch the video as it really is easy. With the new color monitor it should take about 20 - 25 minutes. With the old gray scale monitor add 10 - 15 minutes. Any questions just call and someone will walk you through it! Best CS of any company.